1. Field of the Invention
The present invention relates to a coil, and more particularly, it relates to a coil such as laminate type transformer which is mounted on the printed-circuit board.
2. Description of the Prior Art
As a conventional laminate type coil, there is a coil containing a winding part wherein plural sheets each having a winding pattern are laminated, and the winding patterns formed on the sheets are connected. As shown in FIG. 9, a sheet 1 on which one spiral winding pattern 2 is formed is used in the winding part of the coil. A hole 3 for inserting a core is formed through the sheet 1, and the spiral winding pattern 2 is formed around the hole 3. Both ends of the winding pattern 2 are connected to electrodes on the outside and the inside of the sheet 1.
As shown in FIG. 10, a winding pattern 5 is formed on the other sheet 4. The winding pattern 2 is connected to the winding pattern 5 at the inside of the sheet 1 and the sheet 4. Therefore, a winding is formed between the input/output portions where the winding patterns are connected to electrodes on the outside of the sheet 1 and the sheet 4. Another winding is formed by forming winding patterns whose number of turns are different from above winding patterns on another two sheets, and forming the same structure as above. A transformer is manufactured by coupling the two windings magnetically with a core.
However, in the conventional coil, at least two sheets are required for forming one winding, because the input/output portions for connecting to the external circuit are formed at the outside of the sheets. When the transformer is manufactured, the number of sheets is increased because plural windings are required. Therefore, manufacturing cost of the coil is high, and miniaturization such as forming a thin type coil is difficult.